Auxiliary heaters to aid in activation of cathode ray type guns



Feb. 24, 1959 R. P. STONE 2,875,361

AUXILIARY HEATERS TO AID IN ACTIVATION C ODE RAY TYPE GUNS F" d May 31,1955 a filament adjacent to the cathode surface.

United States Patent 2,875,361 AUXILIARY HEATERS T0 AID IN ACTIVATION 0FCATHODE RAY TYPE GUNS Robert P. Stone, Princeton, N. J., assignor toRadio Corporation of America, a corporation of Delaware Application May31, 1955, Serial No. 511,886 Claims. (Cl. 31385) This invention relatesto. electron guns and particularly to an improved method of and meansfor constructing electron guns for cathode ray tubes.

During the conventional construction of electron guns for cathode raytubes, the cathode is sprayed with a layer of material that includesbarium carbonate and/ or strontium carbonate. After the gun assembly hasbeen placed within the neck portion of an evacuated envelope, the bariumcarbonate and/or strontium carbonate. is converted to the oxide form ofthe material, as this is the active form, and produces an emission ofelectrons when heated to a sufiiciently high temperature during tubeoperation. The barium and strontium oxides are unstable and tend torapidly combine with moisture and carbon dioxide when exposed to theatmosphere. Thus, the cathode is activated after tube evacuation andbefore it is sealed off.

The normal method of activating the barium carbonate and/or strontiumcarbonate on the cathode of an electron gun is to heat the cathode byapplying potentials to When heating the cathode, the control gridelectrode, which is spaced closely adjacent to the cathode, is alsoheated in order to prevent it from collecting various breakdown productsfrom the cathode. The reason for this is that these breakdown productswould re-evaporate back to the cathode when the control electrode isheated during subsequent tubeoperation and would then cause a decreasein electron emission.

In tubes constructed prior to this invention, the usual method ofheating the control grid electrode is by use of a radio frequency coilthat is placed around a neck portion of the envelope. This method ishighly satisfactory for certain types of tubes. However, in other typesof tubes the electron gun is inaccessible to the radio frequency field.

Examples of such tubes are: 1) when the electron gunis supported withina large diameter envelope that does not have a neck; (2) when theelectron gun is.

arranged in such a position that heat from the radio frequency coilwould harm other tube parts before the control grid is suflicientlyheated; (3) when the envelope is metal; and (4) in demountable systems.

It is therefore'an object of this invention to provide a new and novelmethod of and means for heating the control electrode during activationof an electron gun.

comprises a filament, a cathode and a control grid electrode. The heaterelement, is arranged in heat transfer relationship with respect to thecontrol grid electrode.

During tube processing, the cathode of the electron gun is heated, atleast partially, by conventional means in that current is passed throughthe filament to provide heat .to the cathode to decompose the carbonatecoating.

Simultaneously, the grid electrode is heated by passing current throughthe heater element. Thus, electron guns lc Patented Feb. 24, 195-9manufactured in accordance with this invention may be arranged in anydesired position within an envelope since it is not necessary that theybe .accessible to radio frequency heating.

Other features and advantages of this invention will become more clearfrom reading the following specification in conjunction with theaccompanying single sheet of drawings, wherein:

Figure 1 is a transverse sectional view of a storage tube in which thisinvention is particularly applicable;

Figure 2 is an enlarged sectional view of parts of a gun structureutilizing an embodiment of this invention;

Figure 3 is an enlarged fragmentary sectional view of another embodimentof this invention.

Referring now to Figure 1 there is shown a transverse sectional view ofa storage tube 10 utilizing this invenare inaccessible to conventionalelectron gun activating means. Thus, the particular storage tube 10 inFigure 1 is shown merely to illustrate one of many useful applicationsof the present invention.

The storage tube 10 generally comprises, within an evacuated envelope11, an electron gun 113 which is normallyreferred to as a writing gun.The electron gun 13 provides an electron beam 15 which is scanned overan apertured insulating storage target 17 to deposit charges on thestorage target 17. A viewing gun 19 is provided which sprays the storagetarget 17 with electrons. During operation, the electrons from theviewing gun 19 are repelled from the areas of target 17 which are notcharged, or written on, by beam 15. In the areas that have informationwritten thereon, the electrons of the viewing gun 19 pass throughapertures in target 17 to strike a fluorescent screen 21.

As shown more clearly in Figure 2, the cathode is supported within thecontrol grid electrode 27 by means of an insulating spacer 29. Thecontrol grid electrode, or cylinder, 27 has one end closed by means ofan apertured disk member 31. Surrounding the control grid cylinder 27,but insulated therefrom, is a heater 33. Spaced from the closed end ofthe control grid cylinder 27 is a second grid electrode 34.

During the manufacturing of the electron gun 19 the 7 cathode 23 iscoated with a mixture of material that contaminants with respect to theother electrodes, such as oxygen, carbon monoxide, and carbon dioxideare driven from the hot cathode. The contaminants are preferably takeneither out of the envelope by the evacuating pump (not shown), orabsorbed by a getter 36, so that they will not subsequently return tothe cathode and decrease electron emission. However, if the control gridcylinder 27 remains cool during this activation process, thesecontaminants will be deposited upon the control grid cylinder since itis a surface near to the cathode. If the contaminants are deposited onthe control grid cylinder, the first time the control grid is; heatedduringnormal tube operation, .the contaminants on the control grid willbe driven back to the cathode and will react with the materials, i. e.the barium oxide 3 and strontium oxide, so that electron emission fromcathode 23 slumps rapidly and thus the tube life is short due to loss ofelectron emission. It is for this reason that the control grid cylinderis heated during the cathode activation and degassingprocess.

As can be seen from Figure 1 the writing gun 13 is arranged in an offaxis location in the envelope 11 and adjacent to one side thereof. Also,the viewing gun 19 is substantially on the axis of envelope 11 and isspaced from. the walls of envelope 11 a substantial distance. Both of.the electron guns 13 and 19 are thus in such a position within theenvelope 1-1 that it is extremely diflicult to heat the control gridelectrode of the electron guns by the conventional means of a radiofrequency coil. Specifically, if a radio frequency coil were utilized toheat the control grid electrodes in the electron guns 13 and 19, othertube elements might be overheated due to conduction paths which existsin the tubes geometry.

For example, since it is generally necessary to heat a control gridelectrode to a temperature of approximately 700 C. to preventcontaminants from the cathode from settling thereon, an extremely largeamount of power must be utilized inorder to heat the control grid 27 tosuch a temperature. This large amount of power is likely to damage otherelectrodes within the tube, such as those portions of the writing gun 13that are near the envelope Wall, long before the control grid 27 hasattained such a temperature by conventional radio frequency heatingmeans.

In accordance with this embodiment of this invention, the control gridcylinder 27 is heated by current flow through the'heater 33' thatsurrounds the control grid cylinder. in the exampie'presently underconsideration, the heater 33 is made of mil tungsten wire withapproximately four, ormore, turns of the wire around the control gridcylinder 27. A heater similar to heater 33 shown in Figure 2 hasalso'been made of 12 /2 mil thoriated tungsten wire.

During the activation process of manufacturing gun 19, the filament 25is heated-to a temperature of approximately 1300 C. to 1400 C.which-heats the cathode, by meansof radiation and conduction, to atemperature of approximately 1000 C. to 1200- C. Simultaneously theheater 33 is heated to approximately 2200 C. This temperature for heater33 generatessuflicient heat to'raise the temperature of the control gridcylinder 27 to a temperature of approximately 700 C. to 800 C. byradiation. These temperatures may be obtained by passing approximately 6amperes through the heater 33 at a potential'of' approximately 16 volts.The cathode temperature is obtained by passing approXimately 8/10amperes through the filament 25 at a potential of approximately 10 /2volts. In the method just described, the potentials for the heater 33are applied acrossinput terminals 38 and the control grid cylinder 27 isheated solely by heat radiated fromthe heater 33, neglecting the smallamount oflheat radiated to the grid cylinder by the cathode.

Another method of operating the device shown in Figure 2 is to raise thetemperature of heater 33 until it becomes electron-ernissive. When usingthis method, the control grid cylinder 27 is made electricallypositivewith respect to the heater 33 by means of direct current source40. When this method is utilized the control gridcylinder 27 is heatedbyboth electron bombardment and by heat radiation, andthus the heater 33should be at a' temperature that is highly electron-emissive. Forexample, the heater 33 iselectron emissive when raised to atemperatureof approximately 2200 C. for a tungste'n heater, and approximately 1800C. for a-thoriated ment of this invention wherein a heater coil 42 isenclosed'within the control grid cylinder 27' and is-insulated therefromby an insulating coating 44 on the heater, or

auxiliary filament, wires 42. When using this embodiment, a tungsten orthoriated tungsten wire may be utilized, as was previously described,and may be connected to a potential of approximately 6 volts with acurrent of approximately 4 amperes which is sufficient to raise thetemperature of the heater to approximately 1100 C. The particularexample given above as illustrative of this invention causes the controlgrid cylinder 27 to be heated to a temperature of approximately 700 C.to 800 C.

In the embodiment shown in Figure 3, the heat generated by the heater 42is transferred to the control grid cylinder 27' both by radiation and byconduction. Furthermore, some heat will also be transferred to thecathode by radiation, and therefore it is not necessary to apply as muchpower to filament 25' for heating cathode 23' to the same temperaturesas previously described.

Although the invention was decribed with particular reference to theviewing electron gun, it should be understood that it is also applicableto the writing gun 13. Also, the invention was described with particularreference to a storage tube 10 and it should be understood that thistype of tube was shown merely as an example of a particular type oftubewherein this invention is particularly useful.

What is claimed is:

1. An electron gun assembly including a filament, a hollow tubularcathode electrode enclosing said cathode, said hollow tubular gridelectrode having an apertured member spanning one end thereof, and meansincluding a heater element arranged adjacent to said grid electrode andin heat exchange relationship with respect to said grid electrode forheating said grid electrode during cathode activation.

2. An electron gun as in claim 1 wherein said heater is between saidcathode and said grid electrode.

3. An electron gun as in claim 1 wherein said heater surrounds said gridelectrode.

4. An electron gun assembly comprising a filament, a

cylindrical cathode enclosing said'filament and having one end closed,an electrically insulated heater element around said cathode, a controlgrid cylinder enclosing said cathode and said heater, said heater beingadjacent to sai control grid cylinder whereby said control grid isheated by passing currentthrough said heater element.

5. An electron gun assembly comprising a filament a cylindrical cathodeenclosing said filament and havingone end closed, a coating of bariumcarbonate and strontium carbonate on said cathode, a control gridcylinder enclosing said cathode and spaced. therefrom, an auxiliaryheater spaced around said control grid cylinder, said filament being inheat exchange relationship with said cathode whereby said bariumcarbonate and strontium carbonate may be heated bypassing currentthrough said filament, said control grid being in heat exchangerelationship with respect to said auxiliary heater whereby said controlgrid'cylinder may be heated by passing current through said auxiliaryheater, and means for applying potentials between said auxiliary heaterand said control grid cylinder whereby said control grid cylinder mayalso be heated by electron bombardment by electrons from said auxiliaryheater.

References Cited in the file of this patent UNITED STATES PATENTS1,927,812 Thomson Sept. 19, 1933 2,073,804 Pratt Mar. 16, 1937 2,189,993Schenk Feb. 13, 1940 2,401,734 James June 11, 1946 2,413,731 Samuel Jan.7, 1947 2,458,223 Thomas Jan. 4, 1949 2,570,165 Shekels Oct. 2, 19512,671,873 Meier Mar. 9, 1954 2,758,240 ,Szegho Aug. 7, 1956 UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noi 2,875,361February 24, 1959 Robert P. Stone I It is hereby certified that errorappears in the -printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 4, line 28, after enclosing said" insert filament, a hollowtubular grid electrode enclosing said line 44, for sai read said Signedand sealed this 7th day of July 1959.,

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Ofliccr Commissioner ofPatents

